1. Field of the Invention
This invention concerns switching systems. In particular, it relates to the charging of calls originated by stations served by a switching system.
2. Description of the Prior Art
Switching systems designed to interconnect calling telephone stations with called telephone stations are oftentimes provided with automatic message accounting equipment arranged to assess message charges against calling telephone stations. When a telephone station is utilized to originate a call to a called telephone station, the serving switching system accesses automatic message accounting equipment to record an initial entry identifying the calling telephone station, the called telephone station, and the switching system trunk equipment used to establish a call connection. After the call connection has been established, the switching system trunk equipment detects answer of the call by the called telephone station and again accesses the automatic message accounting equipment in order that an answer entry may be recorded identifying the time the call was answered. Subsequently, the switching system trunk equipment detects the disconnect of the telephone stations from the call connection and again accesses the automatic message accounting equipment in order that a disconnect entry identifying the disconnect time of the call connection may be recorded. Thus, on a telephone call the automatic message accounting equipment of a switching system records the called and calling telephone station identities along with the time that the call was answered and the time that the telephone stations disconnected from the call connection. This recorded information is subsequently assembled at a message accounting center to establish a message charge billed to the calling telephone station.
The trunk equipment of a switching system is comprised of a number of trunk circuits, hereinafter referred to as trunks, that are arranged to connect one switching system with another and which are utilized to establish call connections between calling and called telephone stations. Trunks of a switching system bid for the services of a recorder of the automatic message accounting equipment in order that the initial, answer, and disconnect entry information may be entered by the recorder into the memory, magnetic tape, or paper tape of a recorder store. In prior art message accounting systems, trunks requesting the services of a recorder are required to wait until a recorder becomes idle if the recorder is busy servicing another trunk. Since there is a possibility that a trunk may be required to wait for the services of a recorder and it is highly desirable to never overcharge, a time allowance of the maximum time that a trunk may be required to wait for the services of a recorder is deducted from the disconnect time recorded for each call.
In actual usage a number of trunks obtain immediate access to a recorder of the automatic message accounting equipment without waiting. Some trunks obtain access to a recorder after waiting an intermediate interval of time while still other trunks are required to wait for a recorder for the maximum interval of time. Yet, in all cases, the maximum time that a trunk may be required to wait for the services of a recorder is deducted from each recorded call disconnect time thereby accounting for a loss of revenue that is chargeable for the actual time of a call against a calling telephone station.
Some versions of message accounting equipment are arranged to scan the trunks of a switching system to detect the answer and disconnect times of call connections. However, this arrangement involves the additional use of scanner apparatus and requires some means to associate the identity of a trunk with the position of the scanner apparatus in order that the answer and disconnect time of a call connection can be associated with a particular trunk.
Accordingly, a need exists in the art for an automatic message accounting system arranged to adjust the message charging time of a telephone call to compensate for the delay of a call carrying trunk in obtaining access to automatic message accounting equipment. A need also exists for enabling an automatic message accounting system to record a message charging time more closely approximating the actual call handling time of a switching system trunk without requiring the scanning of all the trunks of a switching system.